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13.1 The cause of forces. A force is a___________, or any action that has the ability to change motion. The key word here is action , force______________. 13.1 Units of force. When you measure weight in ________on a scale, you are measuring the force of gravity acting on the object.
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13.1 The cause of forces • A force is a___________, or any action that has the ability to change motion. • The key word here is action, force______________
13.1 Units of force • When you measure weight in ________on a scale, you are measuring the force of gravity acting on the object. • The word “pound” comes from the Latin word_______, which means “weight.”
13.1 The cause of forces • One pound of force equals___________.
13.1 Gravity and weight • ____________________is called weight. • ______________are not the same thing!
13.1 Gravity and weight • A 10-kilogram rock has a ________________no matter where it is in the universe. • A 10-kilogram rock’s _________however, can vary greatly depending on where it is.
13.1 Friction • ____________is a force that resists the motion of objects or surfaces. • Many kinds of ___________exist.
13.1 Friction • Friction depends on____________________________________ • When the hockey puck slides on ice, ______________________________and the ice allows the puck to slide easily.
13.1 Identifying friction forces • Friction is a force, measured in ____________ just like any other force. • Static friction-___________________________________________________
13.1 Identifying friction forces • Sliding friction-_____________________________________________________________________________________
13.1 A model for friction • The greater the force squeezing two surfaces together, ____________________________________________________________________
13.1 Reducing the force of friction • Unless a force is constantly applied, friction ______________________________________________________It is ____________________________friction, but it can be reduced.
13.1 Reducing the force of friction • The friction between a shaft (the long pole in the picture) and an outer part of a machine ___________________. • Friction can be ____________by placing ball bearings between the shaft and the outer part.
13.1 Useful friction • Friction is also important_______________________________. • Grooved tire treads allow space ______________________________________ contact point, allowing for more friction in wet conditions.
13.1 Useful friction • Shoes are designed to increase the friction between their_____________. Why do you think these shoes increase friction? • Players wearing cleats can apply much greater ______ against the ground to help them _____ and to keep from__________.